Impact of cooling rates on the staling behavior of cooked rice during storage

Structural features of rice starch-protein system: Influence of retrogradation time and quick-freezing temperature

This work investigated the effect of retrogradation time (0 h, 2 h, 4 h, 6 h, 8 h) and freezing temperature (-20 °C, -32 °C, -80 °C) on the muti-scale structures of the rice starch-protein system of quick-frozen wet rice noodles. The Relative crystallinity and porosity of the rice starch-protein system increased with increasing retrogradation time. However, while longer retrogradation does lead to an improvement in relative crystallinity, it also results in significant damage to the microstructure. When the retrogradation time was 6 h, the microstructure of the rice starch-protein system was less damaged and the quality was better. The mass fractal dimension and relative crystallinity of the rice starch-protein system exhibited an increase as the freezing temperature was decreased from -20 to -80 °C. Additionally, the retrogradation degree of starch decreased, the size of ice crystals decreased, and the disruption of microforms was reduced. The muti-scale structures of the rice starch-protein systems were similar when quick-frozen at temperatures of -32 and -80 °C. Therefore, the optimal treatment method for practical production is to quick-freeze at -32 °C and age for 6 h to obtain high-quality quick-frozen wet rice noodles.

Systematical construction of rice flavor types based on HS-SPME-GC-MS and sensory evaluation

Rice is one of the main staple foods of Chinese people and its quality requirements are also improving. Aroma is one of the evaluation factors of rice quality, rice with better aroma quality is often more accepted by consumers. A universal aroma descriptive lexicon was established and four flavor types were formed based on samples from 9 representative rice cultivation regions. The key variables affecting the sensory quality of Chinese rice flavor were screened. It was found that the hexanal and nonanal with the highest content had no effect on the flavor properties, which suggests that volatile organic compounds (VOCs) content is not necessarily related to the influence of flavor properties. According to the aroma analysis of different rice flavor types, it can provide guidance for other flavor research.

Volatile Organic Compounds, Evaluation Methods and Processing Properties for Cooked Rice Flavor

Rice (Oryza sativa L.), as the main refined grain in China, has attracted much attention in terms of quality. Rice is usually consumed after cooking, and it is a commonly staple food. Nowdays, people's requirements for cooked rice focus more on the taste characteristics and quality. Furthermore, aroma is one of the primary sensory reference points, which is the most intuitive way for people to judge cooked rice. By integrating and analyzing the researches of cooked rice aroma identification in recent five years, this paper expounds the extraction and identification methods (sensory evaluation method, GC-MS, SPME, MOS sensors, electronic nose, etc.) of the flavor substances in cooked rice, as the processing methods and properties of cooked rice, and the volatile organic compounds of cooked rice under different conditions are summarized as well.

Impact of Low-Temperature Storage on the Microstructure, Digestibility, and Absorption Capacity of Cooked Rice

This study examined the effects of low-temperature storage on the microstructural, absorptive, and digestive properties of cooked rice. Cooked rice was refrigerated and stored at 4 °C for 0.5, 1, 3, 5, and 7 days, as well as frozen and preserved at −20, −40, and −80 °C for 0.5, 1, 3, 5, 7, 14, 21, and 28 days. The results indicated that the stored rice samples generally exhibited a higher absorption capacity for oil, cholesterol, and glucose than the freshly cooked rice. In addition, after storage, the digestibility of the cooked rice declined, namely, the rapidly digestible starch (RDS) content and estimated glycemic index (eGI) decreased, whereas the slowly digestible starch (SDS) and resistant starch (RS) content increased. Moreover, the increment of the storage temperatures or the extension of storage periods led to a lower amylolysis efficiency. Scanning electron microscopy (SEM) analysis indicated that storage temperature and duration could effectively modify the micromorphology of the stored rice samples and their digestion. Moreover, microstructural differences after storage and during simulated intestinal digestion could be correlated to the variations in the absorption capacity and digestibility. The findings from this study will be useful in providing alternative storage procedures to prepare rice products with improved nutritional qualities and functional properties.

Formation of type 3 resistant starch from mechanical activation-damaged high-amylose maize starch by a high-solid method

This study focused on constructing a high-solid reaction system to prepare type 3 resistant starch (RS₃) with high-amylose maize starch as raw material by mechanical activation (MA) pretreatment combined with thermal and freeze-thaw treatments. MA pretreatment effectively destroyed the crystal structure and molecular structure of native starch. MA damaged starch with a certain viscosity could form dough with a small amount of water to construct a starch continuous phase system. RS content increased with the damage levels of starch as the formation of double helix structure, attributed to that the molecules of MA damaged starch could be easy to move and form recrystallization structure. Thermal and freeze-thaw treatments contributed to strong interaction of starch-water and the re-formation of internal crystal structure of MA damaged starch to form RS₃. This study provides insight into the development of a highly effective approach for large scale production of resistant starch.

Effects of cooling rate and complexing temperature on the formation of starch-lauric acid-β-lactoglobulin complexes

The aim of present study was to investigate the effects of cooling rate (3, 5, 10, 15 °C/min) and complexing temperature (50, 60, 70, 80 and 90 °C) on the formation of complexes between wheat starch (WS), lauric acid (LA) and β-lactoglobulin (βLG) in Rapid Visco Analyser (RVA). Higher cooling rate resulted in the higher viscosity peak and final viscosity of WS-LA or WS-LA-βLG complexes than the lower cooling rate during setback of RVA procedure. Results from differential scanning calorimetry (DSC) and Raman spectroscopy showed that larger amount of complexes with lower thermal transition temperatures were formed at higher cooling rate. Higher complexing temperature led to the formation of more complexes with higher thermal transition temperatures. XRD patterns of binary and ternary complexes presented no differences at different cooling rates or different complexing temperatures. We conclude that both higher cooling rate and complexing temperature facilitate the formation of WS-LA and WS-LA-βLG complexes.

Effect of cooling rate on long-term recrystallized crystal of rice starch in the presence of flavor compounds

This study evaluated the effect of cooling rate on starch recrystallization in the presence of 2,3-butanedione and 2-acetyl-1-pyrroline, which could form B-type and V-type complexes with starch, respectively. Rapid cooling resulted in poor perfection and high heterogeneity of both B-type and V-type recrystallized crystal. For B-type crystal, rapid cooling changed nucleation mode from instantaneous (Avrami index n < 1) to continuous mechanism (1 ≤ n ≤ 2), and decreased recrystallization rate from 0.0502 to 0.0160 d^-n, indicating the increased retention of starch on 2,3-butanedione. V-type crystal was formed at initial stages of recrystallization, and inhibited the growth of B-type crystal. The loose crystalline obtained by rapid cooling is conducive to the retention of flavor compounds for B-type complexes (especially ≤14 days) and V-type complexes (especially ≤1 day). These results could provide guidance for maintaining fragrance of instant rice during long-term storage.

Effect of vacuum cooling on stability of macro-porous sausage during refrigerated storage-Vacuum-cooled sausage has a longer shelf life

In this study, two types of cooling methods (vacuum cooling and air cooling) were used to cool cooked macro-porous sausage. Alterations in the microbiological conditions, pH, instrumental color (L*, a*, and b*), total volatile nitrogenous bases (TVB-N), lipid oxidation (TBARS), water activity (aW), moisture content, and texture indicators were evaluated to determine sausages' quality changes during storage under refrigeration for up to 10 days. In general, the shelf life of sausages chilled by vacuum cooling (8 days) was similar to that of sausages cooled by air cooling (9 days). For pH, no significant difference (p > .05) was obtained between two cooling methods. However, vacuum-cooled sausages have lower L* value (p < .05), lower moisture content, and water activity compared with the air-cooled sausages. However, sausages cooled by vacuum cooling showed a sharp increase in TBARS and TVB-N values but maintained texture characteristics for a longer time compared with air-cooled sausages. Although the results indicated that the quality of sausages treated by those two methods remarkably decreased after 7 days, characteristics of sausages cooled by vacuum cooling are better within accepted standards compared with air-cooled sausages. In conclusion, vacuum cooling can be a feasible cooling method with great potential to be used in cooked macro-porous sausages to maintain the quality and may provide reference experiences for the food with similar structure.

Effect of low temperature on the aging characteristics of a potato starch gel

In this work, the freezing curve of a potato starch gel with different concentrations was determined. The water migration, texture, microstructure and gelatinization of a potato starch gel with 8% starch concentration were studied during aging. The results showed that the freezing characteristics of the potato starch gel with different starch concentrations were quite different. NMR results showed that the relaxation time and proportion of water with different existing states (T₂₁, T₂₂ and T₂₃) in the potato starch gel varied significantly under different aging temperatures. Under different aging temperatures, the texture characteristics and the gel strength of the starch gel were significantly different. The water retention of the gel was better under aging temperatures of 3 °C and -3 °C than for other gel samples. SEM and C-cell results showed that under aging temperatures of 3 °C and 0 °C, the formation of a gel network structure was accelerated, and the gel was relatively firm, with small and uniform pores and a larger pore area and number. The rapid viscosity analysis results showed that the peak viscosity, breakdown and setback of the vacuum freeze-dried gel powder changed differently under the aging temperatures.

Influence of Packaging Oxygen Transmission Rate on Physical Characteristics of Frozen Cooked Rice Under Various Freezing Conditions

The influence of packaging oxygen transmission rate (OTR; 0, 3,000, 5,000, 7,000, and 20,000 [mL/m² ]/day) on cooked rice quality factors, including freezing rate and time, moisture content, color parameters, texture characteristics, and morphology, were evaluated. Cooked rice was frozen at -20 and -80 °C using packaging with different OTRs for 14 days. Freezing rates in packaging with lower OTRs (0, 3,000, and 5,000 [mL/m² ]/day) were higher than those in packaging with higher OTRs. The moisture content of cooked rice was the highest in OTR 5,000 packaging under all experimental conditions. Lightness (L^* ) and total color difference (ΔE) values were the highest in OTR 20,000 packaging, whereas ΔE values were the lowest in OTR 5,000 packaging. Hardness and cohesiveness of frozen cooked rice gradually increased from OTR 0 to 5,000 but decreased from OTR 5,000 to 20,000. Morphology was distinct in all conditions and at all OTRs. Thus, we confirmed that the OTR of packaging influences the physical characteristics of frozen cooked rice. Therefore, packaging OTR should be considered when seeking to improve the quality of frozen cooked rice. PRACTICAL APPLICATION: Packaging oxygen transmission rate (OTR) influenced quality characteristics of frozen cooked rice under various freezing conditions. Cooked rice frozen in packaging with lower OTRs (0, 3,000, and 5,000 [mL/m² ]/day) showed higher freezing rates, higher moisture content, shorter freezing times, smaller ice crystal formation, homogeneous pore distribution, and lower total color differences (ΔE) than did cooked rice frozen in packaging with higher OTRs (7,000 and 20,000 [mL/m² ]/day). Packaging OTR influences frozen cooked rice quality characteristics, and should therefore be carefully considered when designing rice products.

Effects of limited moisture content and storing temperature on retrogradation of rice starch

The objective of this study is to investigate the effects of limited moisture content and storing temperature on the retrogradation of rice starch. Starch was gelatinized in various moisture contents (30-42%) and rice paste was stored at different temperatures (4 °C, 15 °C, 30 °C, -18/30 °C and 4/30 °C). X-ray diffraction (XRD) analysis revealed that after retrogradation, the crystalline type of rice starch changed from A-type to B + V type. The B-type crystallinity of retrograded rice starch under 30 °C was the highest among the five temperature conditions, and an increase in B-type crystallinity with increasing moisture content was observed. Differential scanning calorimetry (DSC) results revealed that rice starch retrogradation consists of recrystallization of amylopectin and amylose, and is mainly attributed to amylopectin. The higher moisture content was favorable for amylopectin recrystallization, whereas the moisture content had little effect on the amylose recrystallization. The optimal temperature for amylopectin and amylose recrystallization was 4 °C and 15 °C, respectively. The amylopectin recrystallization enthalpy of rice starch stored at 4/30 °C was mediated between 4 °C and 30 °C but always higher than that at -18/30 °C. On the whole, after being heated at 42% moisture content and stored at 4 °C, rice starch showed the maximum total retrogradation enthalpy (8.44 J/g).

Effect of soaking and cooking on structure formation of cooked rice through thermal properties, dynamic viscoelasticity, and enzyme activity

The quality of cooked rice and its influence factors have always been the focus of researches. However, the formative mechanisms of its eating quality and structural changes of rice during cooking have seldom been evaluated. In this study, sectional real-time cooking was performed by differential scanning calorimetry (DSC) and dynamic viscoelasticity analysis to monitor the phase transitions and mechanical changes of kernels, which exhibited different characteristics in different stages. Both glass transition and pasting behavior were captured, and showed more viscoelasticity of cooked rice at higher soaking temperatures. Meanwhile, the enzyme activity of rice during soaking was successfully measured by a rapid viscosity analyzer (RVA). Along with the differences of morphologies and crystalline structure at different soaking conditions, the findings of DSC and rheometer were further verified. This study provides effective methods to evaluate changes in rice during cooking and explains the mechanism of differences formed by the soaking temperature.

Quality of ready-to-eat komal chawal produced by brown rice parboiling method

Komal chawal, meaning soft rice, produced by brown rice parboiling of a low amylose rice variety chokuwa, was studied for its physical, physico-chemical, morphological and structural characteristics. The product was produced by soaking the brown rice at 60 °C for 90 min, followed by steaming and air drying to 12.0% (wb). The two steaming conditions used were: (1) open-steaming at atmospheric pressure for 20 min and (2) pressure-steaming at 1 atm (gauge) for 10 min. The three different drying temperatures used were 40, 50 and 60 °C. When soaked in water at 60 °C for 20 min the product attained a hardness value of cooked rice. The extent of changes in the kernel and flour properties as compared to the raw form were affected by the severity of the steaming condition and drying air temperature. The pressure steamed samples exhibited virtually persistent growth in paste viscosity in the profiles obtained from the rapid viscosity analyzer. X-ray diffraction analysis of flours revealed a loss of A-type pattern and formation of feeble peaks of A + V-type mixed patterns in steam-treated samples. Scanning electron photomicrographs showed the loss of the polygonal shape by starch granules during processing. The values of rehydration ratio, equilibrium moisture content for rehydration, sediment volume, extent of color change as denoted by total color difference, and the percent head rice yield were higher in pressure steamed komal chawal samples.